Create dataframe from row and colum indexes

Question

Since my previous question went unanswered, I'll try again more simply.

I have a program which makes a list containing row and column indexes:

a = [0, 0, 1, 1] # row
b = [0, 1, 0, 1] # column

This can also be formatted as lists of list:

a = [[0,0], [0,1], [1,0], [1,1]]

Dataframe:

      Name  2544  2543  2542
0     DR01    13    16    23
1     DR02    15    27    12
2     DR03    16    18    13
3     DR04    17    92    56

Objective is to obtain the values from the dataframe mentioned based on indexes in list and create a new dataframe. I tried a for loop but that didn't work and was very slow.

What it should look like:

      Name  2544
0     DR01    13
1     DR02    15

Update:

Here is what I have tried:

In[96]: df = importDialog.df.iloc[a,b]
In[96]: print(df)

Out[96]:
      Name  2544    Name  2544
0     DR01    13    DR01    13
1     DR02    15    DR02    15

Also, when I try showing the complete dataset in a table:

MemoryError: Unable to allocate 9.06 GiB for an array with shape (34749, 34992) and data type object

@QuangHoang I'm planning to add a condition that if the shape is not rectangular, an exception is raised. Could you help me with that? — user6783194
– user6783194, Commented Feb 20, 2020 at 21:13

Quang Hoang · Accepted Answer · 2020-02-20 21:17:02Z

1

Assuming your checked that a,b constitute a rectangular shape:

a = [0, 0, 1, 1] # row
b = [0, 1, 0, 1] # column

df.iloc[sorted(set(a)),sorted(set(b))]

Output:

   Name  2544
0  DR01    13
1  DR02    15

answered Feb 20, 2020 at 21:17

Quang Hoang

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4 Comments

user6783194 Over a year ago

Thanks a ton, been breaking my head with this for almost 2 days. Two more thing, is there a way to do this if the shape is not rectangular? and how would I check if the shape is not rectangular?

Quang Hoang Over a year ago

len(a) == len(set(a)) * len(set(b))

user6783194 Over a year ago

That makes sense. Thanks again. Would vote your answer up, but I don't have enough rep.

Quang Hoang Over a year ago

Also, you need to check if a,b have same length, which might not be the case from your error message.

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